CN108517735B - Durability asphalt pavement design method based on double-modulus theory and pavement structure thereof - Google Patents
Durability asphalt pavement design method based on double-modulus theory and pavement structure thereof Download PDFInfo
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Abstract
The invention discloses a method for designing a durable asphalt pavement based on a double-modulus theory, which introduces the double-modulus theory on the basis of a layered elastic system theory under the load of double-circle vertical uniform distribution, endows corresponding tension-compression modulus according to the difference of stress and tension of each point of the pavement during pavement mechanics calculation, establishes a design method which is more in line with the stress property of the actual pavement, and improves the accuracy of pavement design; the maximum tensile stress of the semi-rigid base layer and the subbase layer bottom of the pavement and the maximum tensile strain of the asphalt surface layer designed according to the method are far less than the fatigue limit, so that the service life of the pavement is greatly prolonged, and the requirement of the durable asphalt pavement is met; the damage of the road surface can only occur on the road surface, the damage mode of the road surface is changed from bottom to top, and only the upper layer needs to be milled or covered during maintenance, so that the maintenance cost is saved.
Description
Technical Field
The invention belongs to the technical field of asphalt pavement design, and particularly relates to a durable asphalt pavement design method based on a double-modulus theory and a pavement structure thereof.
Background
In the nineties, China has achieved great results in the construction practice of high-grade road asphalt pavements. However, from the aspect of the use condition of the asphalt pavement which is put into operation, most of the asphalt pavements which do not reach the service life have serious function attenuation and structural damage, and the reasons are that besides the reasons caused by construction quality and overload, the theoretical system of the structural design has obvious defects and is one of the important reasons.
At present, the design method of the asphalt pavement in China adopts an isotropic layered elastic system theory, and the parameters of each layer of material are compressive resilience modulus during calculation, however, a large number of researches show that the elastic modulus difference of most materials under tension and compression is large, inorganic binders such as road asphalt mixture, cement stable mixture and the like also show the property of unequal tensile and compressive moduli, and the compressive modulus is generally larger than the tensile modulus. The pavement structure has a tensile stress area and a compressive stress area under the action of load, so that the larger compressive resilience modulus is simply applied as the uniform modulus of the material when pavement mechanics calculation is carried out, larger errors exist in the calculation result or the performance of the designed pavement is overestimated, errors generated during calculation cause the failure mode of the pavement set by the asphalt pavement structure design theory to be inconsistent with the typical damage characteristic of the actual pavement, and the strength and rigidity standards adopted in the design can not effectively play a control role.
A lot of studies show that the modulus of many materials shows the property of different tensile modulus and compressive modulus, resulting in the mechanical response of the engineering structure with different characteristics of tensile and compressive stresses, A. Ammbaromellose (A б A ц у M я A.) in 1982 authored the first monograph about the problem of different modulus of tensile and compressive stresses, establishing the theory of the structure based on the difference of modulus of tensile and compressive stresses as the theory of different modulus or the theory of double modulus.
The object of the bi-modal theory is solids and continuum, the object is considered homogeneous and isotropic and is based on small deformation assumptions. A, amebaltrom states: for most of materials with different tensile and compressive elastic moduli, a relation curve of stress and strain can be represented by two straight lines, and a simplified constitutive relation represented by the segmented straight line function has enough precision and completely meets the requirements of engineering application, as shown in fig. 1. In the bi-linear model, the elastic parameters in the constitutive relation of the material are divided into two cases in tension and compression of the principal stress: drawing modulus E when being pulled+And larpoisson ratio mu+Modulus of pressure taking when pressed E-And Poisson ratio μ-Thus, the constitutive equation based on the principal stress direction is established as follows:
in the formula: epsilonα,εβ,εγIs the principal strain, σα,σβ,σγIs principal stress, A is a compliance matrix, and the modulus E and Poisson's ratio μ are determined by respective multiplication of positive and negative properties of principal stress, e.g. σαModulus E > 0αAnd poisson ratio muαGet E+And mu+Otherwise, get E-And mu-。
Disclosure of Invention
The invention aims to provide a durable asphalt pavement design method based on a double-modulus theory and considering different tensile and compression characteristics of pavement materials and a pavement structure thereof.
In order to solve the technical problems, the invention provides a durable asphalt pavement design method based on a double-modulus theory, which comprises the following steps:
step 1, primarily simulating an asphalt pavement structure
On the basis of the existing specification and engineering practice, an asphalt pavement structure is simulated, the design parameters of pavement materials of each structural layer are determined by actually measuring or referring to related specifications and documents, and in any two adjacent contacted structural layers, the compression molding quantity of the structural layer positioned below is greater than or equal to the drawing modulus of the structural layer positioned above, and the compression molding quantity of a roadbed is greater than or equal to the drawing modulus of the structural layer at the bottommost end;
Determining the fatigue limit of each structural layer through fatigue tests of a large amount of road materials or by referring to related documents at home and abroad; taking the fatigue limit of each structural layer and other standards required by the current pavement design specification as design standards;
step 3, establishing a numerical model of the primary asphalt pavement structure
Based on the theory of an elastic layered system under the load of double-circle vertical uniform distribution of the pavement, establishing a numerical model of a preliminary asphalt pavement structure by using finite element software, and initially setting the layer number, the thickness and the material attribute of each structural layer according to the preliminary condition of the step 1;
Introducing a double-modulus theory into the numerical model of the preliminary asphalt pavement structure established in the step 3, compiling a subprogram of a double-modulus constitutive relation based on a secondary development platform of finite element software, endowing each point of the pavement structure with corresponding tension-compression modulus and tension-compression Poisson ratio according to different stress tension-compression states by a numerical method, performing trial calculation, comparing a mechanical response value with a design standard, and completing calculation if the design standard is met; if not, re-executing step 1.
Further, the design parameters include the tension-compression modulus, the tension-compression poisson ratio and the tensile strength.
Further, the modulus of each point of the road surface structure is endowed with corresponding tension-compression modulus and tension-compression poisson ratio according to different stress tension-compression states through a numerical method in the step 4, and the method specifically comprises the following steps:
the first step is as follows: firstly, assuming that the road surface structure has the same modulus, for example, giving the road surface structure initial elastic parameters according to the full-tension or full-pressure state to obtain an initial elastic matrix D+Or D—And then obtaining an initial integral rigidity matrix K0Calculating the stress strain and the node displacement of each unit;
the second step is that: obtaining the principal stress and the principal stress direction of each unit Gaussian integration point according to the calculation result of the previous iteration (i-1 iterations), judging the positive and negative of the principal stress on each integration point, and then obtaining a flexibility matrix A in the principal stress direction of each integration point calculated by the ith iteration according to the formula (1)xThen applying equation (2) to obtain an elastic matrix DxApplying the formula (3) to obtain the rigidity matrix K of the unit with different tensile and compressive moduli under the common rectangular coordinate systemx eFinally integrated as a new global stiffness matrix Kx；
Wherein:
in the formula: epsilonα,εβ,εγIs the principal strain, σα,σβ,σγIs principal stress, A is a compliance matrix, and the modulus E and Poisson's ratio μ are determined by respective multiplication of positive and negative properties of principal stress, e.g. σαModulus E > 0αAnd poisson ratio muαGet E+And mu+Otherwise, get E-And mu-；
D＝A-1Formula (2)
Ke＝∫VBTLTDLBdV type (3)
In the formula (3), B is a strain matrix, L is a conversion matrix of the main stress direction and the common rectangular coordinate direction, T is a matrix conversion symbol, and V is an analysis structure area;
the third step: according to a stiffness matrix KxPerforming the ith iterative calculation to obtain the stress strain or node displacement of each unit;
the fourth step: and (3) comparing the stress or displacement of each unit calculated in the ith iteration (namely the third step) with the stress or node displacement of each unit corresponding to the ith-1, finishing the calculation and stopping the machine if the absolute value of the stress difference or the displacement difference is less than or equal to the convergence control standard value, increasing i by 1 (namely i +1) if the absolute value of the stress difference or the displacement difference is not met, and returning to the second step to perform the next iteration calculation until the convergence control standard is met. Wherein i in the above steps represents the number of iterations.
Further, the primarily-planned asphalt pavement structure in the step 1 comprises an asphalt surface layer, a cement-stabilized macadam base layer, a cement-stabilized macadam subbase layer, a macadam cushion layer and a roadbed, and when the number of layers, the thickness and selected materials of the structure layer are designed, the modulus of the roadbed is properly improved on the basis of properly improving and strengthening compaction of roadbed soil; the modulus of the cement stabilized macadam base is properly reduced, so that the purpose of reducing the modulus difference between the base and the surface course and the cushion course is achieved; meanwhile, the tensile-compression modulus ratio of the cement stabilized macadam base layer is properly increased so as to reduce the number of paving layers of the base layer and the lower layers, and the modulus, particularly the compression molding amount, of the asphalt surface layer is properly increased so as to reduce the tensile strain of the surface layer.
Furthermore, the number of the layers of the asphalt surface layers in the preliminary simulation asphalt pavement structure is required to be more than or equal to 2, the total thickness of the asphalt surface layers is more than or equal to 15cm, the compression modulus of each asphalt surface layer is more than or equal to 1500MPa, and the tensile modulus is more than or equal to 1200 MPa.
Further, the laminated modulus range of the cement stabilized macadam subbase in the primary asphalt pavement structure is required to be 1000-3500MPa, and the tensile modulus range is required to be 200-1500 MPa; the thickness of each cement stabilized macadam subbase layer is more than or equal to 15 cm;
the number of the layers of the cement-stabilized macadam base layer is more than or equal to 2, the range of the compression modulus is 2000-6000MPa, and the range of the drawing modulus is 400-4000 MPa; the thickness of each layer is more than or equal to 15 cm.
Furthermore, the compression molding amount range of each gravel cushion layer in the primary asphalt pavement structure is required to be 200-1500MPa, the tensile molding amount range is required to be 20-250MPa, and the thickness is more than or equal to 15 cm.
Furthermore, the compression molding amount of the roadbed required in the preliminary asphalt pavement structure is 80-120 MPa.
Further, when the numerical model of the preliminary asphalt pavement structure is established in the step 3, the method also comprises a step of verifying the correctness of the model by comparing the calculation result with a calculation result of the BISAR3.0 based on the same modulus theory.
Further, the finite element software is commercial finite element software ABAQUS.
Further, the secondary development platform adopts a UMAT platform on ABAQUS.
A pavement structure is designed by adopting the design method of the durable asphalt pavement based on the double-modulus theory, and comprises an AC13-I upper surface layer, an AC20-I middle surface layer, an AC25-I lower surface layer, 3.5-4% of a cement-stabilized macadam base layer, 2.5-3.5% of the cement-stabilized macadam base layer, 1.5-2.5% of the cement-stabilized macadam base layer, 0.5-1.5% of the cement-stabilized macadam subbase layer, a cushion layer and a roadbed from top to bottom; wherein the thickness of the upper layer of the AC13-I is 4 cm; the thickness of the surface layer in the AC20-I is 6 cm; the thickness of the lower layer of the AC25-I is 8 cm; 3.5% -4% of the cement stabilized gravel layer is 18cm thick; 2.5% -3.5% of the cement stabilized gravel layer is 18cm thick; 1.5-2.5% of cement stabilized macadam underlayer with a thickness of 20 cm; 0.5% -1.5% of the cement stabilized macadam subbase layer is 15cm thick; the cushion layer consists of a high-quality grade gravel cushion layer with the thickness of 15 cm.
Compared with the existing asphalt pavement design method, the asphalt pavement design method based on different modulus theories has the following outstanding advantages:
1) different modulus theories are introduced, different tensile and compression characteristics of materials are considered in the design parameters of the pavement, corresponding tensile and compression moduli are respectively endowed according to different stress tensile and compression properties during calculation, the actual stress condition of the pavement is better met, and the accuracy of pavement design is improved.
2) The fatigue limit of the asphalt surface layer and the water stabilization base layer is introduced, and the maximum value of the mechanical response of the most unfavorable point position of the structural layer is smaller than the fatigue limit through combination design, so that the service life of the pavement is greatly prolonged, and the requirement of the durable asphalt pavement is met.
3) The method changes the pavement damage mode from bottom to top from top to bottom, so that the pavement damage is firstly generated on the road surface or the upper part of the surface layer, and only milling or finishing the road surface is needed during maintenance and repair, thereby saving the maintenance cost and being convenient to repair.
4) The invention has important significance for promoting the development of the asphalt pavement design method, perfecting the asphalt pavement design theory and design index and improving the durability of the asphalt pavement.
Drawings
FIG. 1 is a schematic diagram of the constitutive relation of different tensile and compressive moduli;
FIG. 2 is a flow chart of bituminous pavement design based on a double modulus theory;
FIG. 3 is the tensile modulus and compression modulus test results for road asphalt;
FIG. 4 is a graph showing the tensile modulus and compression modulus of cement stabilized macadam mixtures as a function of cement dosage;
FIG. 5 is a flow of a finite element calculation for a dual-modulus problem;
FIG. 6 is a comparison of the road surface deflection of an embodiment of the present invention compared to a typical semi-rigid base asphalt pavement structure;
FIG. 7 is a comparison of the preferred embodiment of the present invention with the road surface maximum horizontal tensile stress of a typical semi-rigid base asphalt pavement structure;
FIG. 8 is a comparison of the preferred embodiment of the present invention versus the road surface maximum horizontal tensile strain of a typical semi-rigid base asphalt pavement structure;
FIG. 9 is a comparison of maximum horizontal tensile strain within an asphalt overlay of a typical semi-rigid base asphalt pavement structure according to a preferred embodiment of the present invention;
FIG. 10 is a comparison of maximum horizontal tensile stress for a preferred embodiment of the present invention compared to a typical semi-rigid base asphalt pavement structure;
FIG. 11 is a comparison of the wheel load center vertical stress of a preferred embodiment of the present invention compared to a typical semi-rigid base asphalt pavement structure.
Detailed Description
The present invention will now be described in detail with reference to the accompanying drawings and examples.
Referring to fig. 2, a method for designing a durable asphalt pavement based on a double modulus theory includes the following steps:
step 1, primarily simulating an asphalt pavement structure
On the basis of the existing specification and engineering practice, the bituminous pavement structure is simulated, the design parameters such as the tensile modulus and the compression modulus of pavement materials of each structural layer are determined by actually measuring or referring to the relevant specification and documents, and in any two adjacent contacted structural layers, the compression modulus of the structural layer positioned below is more than or equal to that of the structural layer positioned above, and the compression modulus of the roadbed is more than or equal to that of the structural layer at the bottommost end;
specifically, the preliminary designed asphalt pavement structure comprises an asphalt surface layer, a cement-stabilized macadam base layer, a cement-stabilized macadam subbase layer, a macadam cushion layer and a roadbed, and when the number of layers, the thickness and the selected materials of the structure layer are designed, the modulus of the roadbed is properly improved on the basis of properly improving and strengthening compaction of roadbed soil; the modulus of the cement stabilized macadam base is properly reduced, so that the purpose of reducing the modulus difference between the base and the surface course and the cushion course is achieved; meanwhile, the tensile-compression modulus ratio of the cement stabilized macadam base layer is properly increased so as to reduce the number of paving layers of the base layer and the lower layers, and the modulus, particularly the compression molding amount, of the asphalt surface layer is properly increased so as to reduce the tensile strain of the surface layer.
Determining the fatigue limit of each structural layer through fatigue tests of a large amount of road materials or referring to related documents at home and abroad, wherein the fatigue limit tensile stress of the cement stabilized macadam base layer and the subbase layer and the fatigue limit tensile strain of the asphalt surface layer are mainly used; taking the fatigue limit of each structural layer and other standards required by the current pavement design specification as design standards;
research shows that the fatigue limit of common asphalt mixture is 70 mu epsilon, and that of modified asphalt mixtureThe fatigue limit is 100. mu. epsilon. Calculating the fatigue limit tensile stress of the cement stabilized gravel layer (including base layer and subbase layer) according to the method specified by the current asphalt pavement design specification, for example, the allowable tensile stress of the cement stabilized gravel layer with the design life of 50 years is the fatigue limit stress of the water stabilized gravel, and the cumulative standard action frequency calculated according to the extra-heavy traffic grade is 6.98 multiplied by 109And performing inverse calculation according to a formula B.2.1-1 of asphalt pavement design Specification (JTGD50-2017) to obtain the allowable tensile stress of the cement stabilized gravel layer, wherein the calculation result is shown in a table 3, the allowable tensile stress is the fatigue limit tensile stress of the cement stabilized gravel layer, and other design standards are the same as the current design Specification.
Step 3, establishing a numerical model of the primary asphalt pavement structure
Based on the theory of an elastic layered system under the condition that the double circles of the pavement are vertically and uniformly loaded, establishing a preliminary asphalt pavement structure numerical model by using ABAQUS finite element software, and initially setting the layer number, the thickness and the material properties of each structural layer according to the preliminary condition of the step 1, wherein the material properties comprise a tensile modulus, a compressive modulus, a Lapoisson ratio and a Press poisson ratio.
Introducing a double-modulus theory into the numerical model of the preliminary asphalt pavement structure established in the step 3, compiling a subprogram of a double-modulus constitutive relation based on a UMAT secondary development platform of ABAQUS finite element software, endowing each point of the pavement structure with corresponding tension-compression modulus and tension-compression Poisson ratio according to different stress-tension-compression states by a numerical method, performing trial calculation, comparing a mechanical response value with a design standard, and finishing the calculation if the mechanical response value meets the design standard; if not, re-executing step 1.
The method has the advantages that the modulus of each point of the road surface structure is endowed with the corresponding tension-compression modulus and tension-compression Poisson ratio according to the difference of the stress-tension-compression states through a numerical method, the problem of different moduli belongs to a special nonlinear problem after bilinear simplification based on constitutive relation, the elastic parameters of the structures with different moduli for tension and compression are related to the stress state of the unit, and the method is suitable for solving by adopting an iterative technique. The method comprises the following steps of judging the main stress state of a unit by using the result of the previous calculation to obtain a corresponding elastic matrix, and then performing the next iteration, wherein the iteration format is as follows:
Ki-1uif type (4)
In the formula (4), Ki-1The global stiffness matrix for the i-1 th iteration, uiAnd (4) a structural node displacement array of the ith iteration. F is an externally loaded array.
Referring to fig. 3, the specific steps are as follows:
the first step is as follows: firstly, assuming that the road surface structure has the same modulus, for example, giving the road surface structure initial elastic parameters according to the full-tension or full-pressure state to obtain an initial elastic matrix D+Or D—And then obtaining an initial integral rigidity matrix K0And calculating the stress strain and the node displacement of each unit.
The second step is that: obtaining the principal stress and principal stress direction of each unit Gaussian integration point according to the calculation result of the previous iteration (i-1 iterations), judging the positive and negative of the principal stress on each integration point, and then obtaining a flexibility matrix A in the principal stress direction of each integration point calculated by the i iterations according to the formula (1)xThen applying equation (2) to obtain an elastic matrix DxApplying the formula (3) to obtain the rigidity matrix K of the unit with different tensile and compressive moduli under the common rectangular coordinate systemx eFinally integrated as a new global stiffness matrix Kx；
Wherein:
in the formula: epsilonα,εβ,εγIs the principal strain, σα,σβ,σγIs principal stress, A is a compliance matrix, and the modulus E and Poisson's ratio μ are determined by respective multiplication of positive and negative properties of principal stress, e.g. σαModulus E > 0αAnd poisson ratio muαGet E+And mu+Otherwise, get E-And mu-；
D＝A-1Formula (2)
Ke＝∫VBTLTDLBdV type (3)
In the formula (3), B is a strain matrix, L is a conversion matrix of the main stress direction and the common rectangular coordinate direction, T is a matrix conversion symbol, and V is an analysis structure area;
the third step: according to a stiffness matrix KxPerforming the ith iterative calculation to obtain the stress strain or node displacement of each unit;
the fourth step: comparing the stress or node displacement of each unit iteratively calculated in the ith (i.e. the third step) with the stress or node displacement of each unit corresponding to the ith-1, and if the absolute value of the stress difference or the displacement difference is less than or equal to the convergence control standard value (10)-8) And if the calculation is not satisfied, increasing i by 1 (namely i ═ i +1), and returning to the second step to perform the next iterative calculation until the convergence control standard is satisfied. Wherein i in the above steps represents the number of iterations. The number of the layers of the asphalt surface layers in the primary asphalt pavement structure is required to be more than or equal to 2, the total thickness of the asphalt surface layers is more than or equal to 15cm, the compression modulus of each asphalt surface layer is more than or equal to 1500MPa, and the tensile modulus is more than or equal to 1200 MPa. The compression molding amount range of each gravel cushion layer in the primary asphalt pavement structure is required to be 200-1500MPa, the tensile molding amount range is 20-250MPa, and the thickness is more than or equal to 15 cm. The laminated modulus range of the cement stabilized macadam subbase in the primary asphalt pavement structure is required to be 1000-3500MPa, and the tensile modulus range is required to be 200-1500 MPa; the thickness of each cement stabilized macadam subbase layer is more than or equal to 15 cm; the number of the layers of the cement-stabilized macadam base layer is more than or equal to 2, the range of the compression modulus is 2000-6000MPa, and the range of the drawing modulus is 400-4000 MPa; the thickness of each layer is more than or equal to 15 cm. In order to enable each structural layer to meet the modulus matching requirement in the step 1, when the pavement material of each structural layer of the preliminary asphalt pavement structure is adjusted, the modulus of each structural layer is adjusted by changing one or more of the mixing proportion, the gradation, the asphalt content or the cement dosage and the compaction mode so as to meet the modulus matching requirement of the invention.
The following is a preferred embodiment of a pavement structure designed using the design method of the present invention, and the applicant has shown through a number of laboratory tests that: the compression molding amount of the mixture such as asphalt mixture and cement-stabilized macadam mixture is larger than the tensile modulus. The test results of the tensile and compressive moduli of several common asphalt mixtures are shown in fig. 4. In FIG. 4, the AC13, AC20 and AC25 are suspension dense-graded asphalt mixtures commonly used for asphalt pavements, and the asphalt used is 70# common base asphalt; the AC13-I, AC20-I and the AC25-I are optimized asphalt mixture, the gradation is skeleton compact type, and the used asphalt is high-performance modified asphalt. Through tests, the change response relation of the tensile modulus and the compressive modulus of the suspension compact type cement stabilized macadam mixture commonly used in road engineering along with the dosage of cement is tested, so that the ranges of the tensile modulus and the compressive modulus and the range of the tensile modulus-compressive modulus ratio are determined, and the test results are shown in fig. 5. This example adjusts the modulus of each water-stabilized macadam layer by changing the cement dosage of the cement-stabilized macadam. The designed asphalt pavement structure and its calculated parameters are shown in table 1, and the typical semi-rigid base asphalt pavement structure (comparative example) and its calculated parameters are shown in table 2.
The mechanical response of the two pavement structures is shown in detail in fig. 6-11. Table 3 shows the mechanical response values corresponding to the key design indexes corresponding to the two road surface structures, and as can be seen from table 3 and fig. 6 to 11, in terms of relative values, compared with the common road surface structure, the mechanical response values of the key design indexes are greatly reduced except that the reduction of the top vertical compressive stress of the surface layer is not obvious in the preferred embodiment. The tensile stress of the cement stabilized macadam base layer is reduced by 27.3%, the tensile stress of the cement stabilized macadam base layer is reduced by 92%, the tensile stress is almost one order of magnitude smaller than that of a common pavement structure and is far smaller than the corresponding fatigue limit stress, and the tensile stress of the base layer of the common pavement structure is larger than the corresponding fatigue limit tensile stress. Therefore, the pavement structure of the present preferred embodiment is almost infinitely long in life when only the influence of the load thereon is taken into consideration, and can achieve the purpose of a so-called long-life or durable base course; meanwhile, the pavement damage caused by the cracking of the base layer, such as a bottom-up damage mode of reflection cracks and the like, can be effectively prevented.
Table 1 asphalt pavement structure of preferred embodiment
TABLE 2 typical semi-rigid base asphalt pavement structure
TABLE 3 comparison of the key mechanical index maximum values for the preferred embodiment and the common pavement structure
Note: the longitudinal direction in table 3 is the driving direction, the transverse direction is the horizontal direction perpendicular to the longitudinal direction, and the vertical direction is the gravity direction.
The maximum horizontal tensile strain in the asphalt surface course is reduced from 71.5 mu epsilon to 30.5 mu epsilon by 57.3 percent, and the maximum tensile strain of the structure is calculated by trial and calculation to be far less than the fatigue limit of the asphalt layer, so the aim of durability is also fulfilled under the condition of only considering the load. The maximum horizontal tensile strain of the road surface is reduced from 128.7 mu epsilon to 73 mu epsilon, is reduced by 39.2 percent and is smaller than the fatigue limit of 100 mu epsilon, road surface cracking caused by overlarge tensile strain of the road surface is greatly prevented, even if cracks are damaged, the mode is from top to bottom, namely, the damage is generated on the upper layer, after the damage is generated, only the upper layer needs to be replaced, and the maintenance of the road surface is easy to realize.
The vertical compressive stress at the top of each structural layer of the surface layer is slightly reduced, but the reduction amplitude can be ignored, and simultaneously, the capability of resisting high-temperature deformation or permanent deformation of the designed structure can be improved because the designed structure adopts the modified asphalt. The deflection of the pavement structure of the preferred embodiment is reduced by 20.4%, indicating that the overall stiffness of the pavement is enhanced.
The above examples are merely illustrative for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. Nor is it intended to be exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (10)
1. A method for designing a durable asphalt pavement based on a double-modulus theory is characterized by comprising the following steps:
step 1, primarily simulating an asphalt pavement structure
On the basis of the existing specification and engineering practice, an asphalt pavement structure is simulated, the design parameters of pavement materials of each structural layer are determined by actually measuring or referring to related specifications and documents, and in any two adjacent contacted structural layers, the compression molding quantity of the structural layer positioned below is greater than or equal to the drawing molding quantity of the structural layer positioned above, and the compression molding quantity of the roadbed is greater than or equal to the drawing molding quantity of the structural layer at the bottommost end;
step 2, determining design standard
Determining the fatigue limit of each structural layer through fatigue tests of a large amount of road materials or by referring to related documents at home and abroad; taking the fatigue limit of each structural layer and other standards required by the current pavement design specification as design standards;
step 3, establishing a numerical model of the primary asphalt pavement structure
Based on the theory of an elastic layered system under the load of double-circle vertical uniform distribution of the pavement, establishing a numerical model of a preliminary asphalt pavement structure by using finite element software, and initially setting the layer number, the thickness and the material attribute of each structural layer according to the preliminary condition of the step 1;
step 4, numerical model calculation
Introducing a double-modulus theory into the numerical model of the preliminary asphalt pavement structure established in the step 3, compiling a subprogram of a double-modulus constitutive relation based on a secondary development platform of finite element software, endowing each point of the pavement structure with corresponding tension-compression modulus and tension-compression Poisson ratio according to different stress tension-compression states by a numerical method, performing trial calculation, comparing a mechanical response value with a design standard, and completing calculation if the design standard is met; if not, re-executing step 1.
2. The method for designing a durable asphalt pavement based on the double modulus theory as claimed in claim 1, wherein: in the step 4, the modulus of each point of the pavement structure is endowed with corresponding tension-compression modulus and tension-compression Poisson ratio according to different stress tension-compression states by a numerical method, and the method specifically comprises the following steps:
the first step is as follows: firstly, assuming that the road surface structure is of the same modulus, giving the road surface structure initial elastic parameters according to the full-tension or full-pressure state to obtain an initial elastic matrix D+Or D—And then obtaining an initial integral rigidity matrix K0(ii) a Calculating to obtain the stress strain of each unit and the displacement of the node;
the second step is that: obtaining the principal stress and principal stress direction of each unit Gaussian integration point according to the i-1 iteration calculation result, judging the positive and negative of the principal stress on each integration point, and then obtaining a flexibility matrix A in the principal stress direction of each integration point according to the formula (1)xThen applying equation (2) to obtain an elastic matrix DxApplying the formula (3) to obtain the rigidity matrix K of the unit with different tensile and compressive moduli under the common rectangular coordinate systemx eFinally integrated as a new global stiffness matrix Kx；
Wherein:
in the formula: epsilonα,εβ,εγIs the principal strain, σα,σβ,σγIs principal stress, A is a compliance matrix, and the modulus E and Poisson's ratio μ are determined by respective multiplication of positive and negative properties of principal stress, e.g. σαModulus E > 0αAnd poisson ratio muαGet E+And mu+Otherwise, get E-And mu-；
D＝A-1Formula (2)
Ke＝∫VBTLTDLBdVFormula (3)
In the formula (3), B is a strain matrix, L is a conversion matrix of the main stress direction and the common rectangular coordinate direction, T is a matrix conversion symbol, and V is an analysis structure area;
the third step: according to a stiffness matrix KxPerforming iterative computation for i times to obtain the stress strain of each unit and the displacement of the node;
the fourth step: comparing the stress or displacement of each unit obtained by the iterative computation of the i times with the stress or displacement of each unit corresponding to the iterative computation of the (i-1) th time, if the absolute value of the stress difference or the displacement difference is less than or equal to the convergence control standard, finishing the calculation and stopping the machine, if the absolute value of the stress difference or the displacement difference is not more than the convergence control standard, increasing 1 (i.e. i is i +1) by i, returning to the second step for the next iterative computation until the convergence control standard is met; wherein i in the above steps represents the number of iterations.
3. The method for designing a durable asphalt pavement based on the double modulus theory as claimed in claim 1, wherein: the primarily-planned asphalt pavement structure in the step 1 comprises an asphalt surface layer, a cement-stabilized macadam base layer, a cement-stabilized macadam subbase layer, a macadam cushion layer and a roadbed, and when the number of layers, the thickness and selected materials of each structural layer are designed, the modulus of the roadbed is improved on the basis of improving and strengthening compaction of roadbed soil; the modulus of the cement stabilized macadam base layer is reduced, so that the purpose of reducing the modulus difference between the base layer and the surface layer and between the base layer and the cushion layer is achieved; and meanwhile, the tensile-compression modulus ratio of the cement stabilized macadam base layer is increased so as to reduce the number of the paved layers of the base layer and the layers below, and the compression molding amount of the asphalt surface layer is increased so as to reduce the tensile strain of the surface layer.
4. The method of designing a durable asphalt pavement based on the double modulus theory as claimed in claim 3, wherein: the number of the layers of the asphalt surface layers in the primary asphalt pavement structure is required to be more than or equal to 2, the total thickness of the asphalt surface layers is more than or equal to 15cm, the compression modulus of each asphalt surface layer is more than or equal to 1500MPa, and the tensile modulus is more than or equal to 1200 MPa.
5. The method of designing a durable asphalt pavement based on the double modulus theory as claimed in claim 3, wherein: the laminated modulus range of the cement stabilized macadam subbase in the primary asphalt pavement structure is required to be 1000-3500MPa, and the tensile modulus range is required to be 200-1500 MPa; the thickness of each cement stabilized macadam subbase layer is more than or equal to 15 cm;
the number of the layers of the cement-stabilized macadam base layer is more than or equal to 2, the range of the compression modulus is 2000-6000MPa, and the range of the drawing modulus is 400-4000 MPa; the thickness of each layer is more than or equal to 15 cm.
6. The method of designing a durable asphalt pavement based on the double modulus theory as claimed in claim 3, wherein: the compression molding amount range of each gravel cushion layer in the primary asphalt pavement structure is required to be 200-1500MPa, the tensile molding amount range is 20-250MPa, and the thickness is more than or equal to 15 cm.
7. The method for designing a durable asphalt pavement based on the dual modulus theory according to any one of claims 1 to 3, wherein: the compression molding amount of the roadbed required in the primary asphalt pavement structure is 80-120 MPa.
8. The method for designing a durable asphalt pavement based on the dual modulus theory according to any one of claims 1 to 3, wherein: and 3, when the numerical model of the preliminary simulation bituminous pavement structure is established, the step of verifying the correctness of the model by comparing the numerical model with a calculation result of BISAR3.0 based on the same modulus theory is also included.
9. The method for designing a durable asphalt pavement based on the dual modulus theory according to any one of claims 1 to 3, wherein: the finite element software adopts commercial finite element software ABAQUS, and the secondary development platform adopts a UMAT platform on the ABAQUS.
10. A pavement structure, characterized in that: the durable asphalt pavement design method based on the double-modulus theory, which is designed by adopting the durable asphalt pavement design method based on the double-modulus theory, as claimed in any one of claims 1 to 9, and comprises an AC13-I upper surface layer, an AC20-I middle surface layer, an AC25-I lower surface layer, 3.5 to 4 percent of cement-stabilized macadam base layer, 2.5 to 3.5 percent of cement-stabilized macadam base layer, 1.5 to 2.5 percent of cement-stabilized macadam base layer, 0.5 to 1.5 percent of cement-stabilized macadam base layer, a cushion layer and a roadbed from top to bottom;
wherein the thickness of the upper layer of the AC13-I is 4 cm; the thickness of the surface layer in the AC20-I is 6 cm; the thickness of the lower layer of the AC25-I is 8 cm; 3.5 to 4 percent of the cement stabilized macadam foundation is 18cm thick; 2.5-3.5% of the cement stabilized macadam foundation is 18cm thick; 1.5-2.5% of cement stabilized macadam foundation with thickness of 20 cm; 0.5% -1.5% of the cement stabilized macadam subbase layer is 15cm thick; the cushion layer consists of a high-quality grade gravel cushion layer with the thickness of 15 cm;
the percentage refers to the percentage of the mass of the cement in the mass of the cement stabilized macadam base or the cement stabilized macadam subbase.
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| CN109989317A (en) * | 2019-04-10 | 2019-07-09 | 长沙理工大学 | A kind of load transfer formula semi-rigid base asphalt pavement structure |
| CN110110495B (en) * | 2019-06-10 | 2022-11-25 | 交通运输部公路科学研究所 | Inverse calculation method for synchronously determining asphalt pavement structure layer modulus and asphalt surface layer Poisson ratio |
| CN110334473B (en) * | 2019-07-16 | 2023-04-07 | 长沙理工大学 | Method for calculating relative deflection of asphalt pavement structure based on modulus decay |
| CN110658086B (en) * | 2019-08-31 | 2022-05-27 | 长沙理工大学 | Asphalt pavement load response analysis method considering tension-compression modulus difference |
| CN112685930A (en) * | 2020-12-22 | 2021-04-20 | 江苏中路工程技术研究院有限公司 | Asphalt pavement structure reinforcement strategy determination method |
| CN112765825B (en) * | 2021-01-27 | 2022-07-08 | 长沙理工大学 | Roadbed surface displacement response determination method considering modulus nonlinear distribution |
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